System for controlling the exhalation pressure of a diver for diving ventilation equipment

ABSTRACT

A system for controlling the exhalation pressure of a diver for diving equipment with a ventilation circuit, includes a unidirectional valve acting on an exhalation outlet of the ventilation circuit, and a brake configured to exert an adjustable constraint on the unidirectional valve in order to control the pressure of the gas from the exhalation outlet so as to generate a positive exhalation pressure in the ventilation circuit of the equipment and thus prevent or treat immersion pulmonary edemas.

The invention relates to diving devices and more particularly to a device for the ventilation part of diving systems to prevent and participate in the treatment of immersion pulmonary edema.

Immersion pulmonary edema is an increasingly frequent pathology secondary to a cardiac decompensation consecutive to the impact of a constraining environment on a diver. What happens is that immersion brings about a phenomenon of containment of the soft tissues, namely of the lower limbs and of the abdomen, with the peripheral blood volumes being redistributed toward the thorax. The cold, combined with the immersion, causes a closing of the blood vessels and slows the heart rate. The increase in the quantity of oxygen brought about by the increase in ambient pressure as the diver gradually descends exacerbates the abovementioned phenomena and reduces the force with which the heart muscle contracts. These respective mechanisms overload the heart and, when the cardiovascular system is defective or aging, this leads to an early leakage of blood liquid into the lungs. Pulmonary congestion, also referred to as pulmonary edema, then leads to a reduction in the oxygenation of the blood and this can rapidly lead to sickness.

A better understanding of this pathology and the recent expansion in leisure diving are behind a marked increase in the number of cases of immersion pulmonary edema. It has even become the second greatest cause of diving accident, just after desaturation accident, and is also the prime cause of death among the divers. Indeed immersion pulmonary edema is actually the prime factor in around 45% of diving cardiac arrests. The onset of immersion pulmonary edema occurs during the first twenty minutes of the dive and worsens during the reascent with the change in position of the diver and therefore change in ventilatory pressure regimes.

The physiopathology of immersion pulmonary edema has been little-understood for a long time. However, the discovery of the cardio-circulatory contribution to the physiopathology (Louge et al., “Pathophysiological and diagnostic implications of cardiac biomarkers and antidiuretic hormone release in distinguishing immersion pulmonary edema from decompression sickness”, Medicine (Baltimore), 95(26): e4060, June 2016), of the rapid worsening of the symptomatology as the diver becomes more vertical, leading to a drop in the expiratory back-pressure (Coulange et al., “Pulmonary edema in healthy SCUBA divers: new physiopathological pathways”, Clin. Physiol. Funct. Imag., 30(3): 181-186, 2010) and of similarities with drowning have made it possible to demonstrate the benefit of envisioning preventing and treating immersion pulmonary edema by generating a positive expiratory pressure (Michelet et al., “Acute respiratory failure after drowning: a retrospective multicenter survey”, Eur. J. Emerg. Med., 2015). The positive expiratory pressure is the expiratory pressure maintained within the airways. It allows the formation of a collapse (collapsing of the lung tissue as a result of the pressure exerted by pleural effusion, a tumor or pneumothorax) to be prevented. In addition, by increasing the space of time during which gaseous exchanges between alveolus and capillary occur, it also allows atelectasis (contraction of the pulmonary alveoli) to be avoided.

Document US 1984/4436090 discloses a ventilation regulating device comprising a piston which is able to exert pressure on a valve, the valve serving to control the flow of gas on inhalation and expiration of an individual for a medical application (a respirator or a resuscitator). This device is able to supply a positive expiratory pressure and can also be used for aeronautical ventilation assistance applications. Document US 2004/035414 discloses a ventilation device for diving equipment, notably for snorkeling, able to supply a positive expiratory pressure. This device makes it possible to slow the ventilation cycle of the diver, balance ventilation work between inhalation and expiration and minimize the risk of development of atelectasis. However, neither one of these two devices is able to prevent or treat immersion pulmonary edema.

Other documents (EP 1500586, US 1993/5259374) disclose adjustable devices for regulating the ventilation of the diver on inhalation, but do not generate a positive expiratory pressure and are therefore unable to prevent or treat immersion pulmonary edema.

The invention seeks to overcome the aforementioned problems of the prior art and more particularly seeks to propose a device that allows the prevention and treatment of immersion pulmonary edema by generating a variable positive expiratory pressure. According to the invention, this prevention device is able to generate an adjustable positive expiratory pressure and thus control the expiratory pressure of the diver for diving ventilation equipment. It comprises a one-way valve acting on the expiratory outlet of the ventilation equipment and a brake configured to apply an adjustable constraint to the valve so as to control the pressure of the gas coming from the expiratory outlet, and therefore of the gas exhaled by the diver. With the invention, the diver may for example benefit from a greater or lesser resistance to expiration in order to prevent the risk of immersion pulmonary edema during exertions immersed in cold water at a great depth. On the other hand, the diver can immediately cancel this resistance to expiration in the event of an emergency reascent in order to prevent a risk of thoracic barotrauma (or pulmonary overpressure) associated with the abrupt expansion of the gas contained in the lungs.

One subject of the invention is therefore a system for controlling the expiratory pressure of a diver for diving equipment having an expiratory circuit. The system comprises a one-way valve acting on an expiratory outlet of the ventilation circuit, and a brake configured to apply an adjustable constraint to the one-way valve so as to control the pressure of the gas coming from the expiratory outlet so as to generate a positive pressure in the breathing circuit of the diving equipment.

According to particular embodiments of the invention:

-   -   the brake may be an adjustable discharge valve comprising a         loading spring and a calibration screw allowing the resistance         of the spring to be adjusted;     -   the system may comprise a release system allowing the brake to         be deactivated, which system may be made up of a central tubular         rod coaxial with the calibration screw;     -   the system may comprise a pressure sensor sensing pressure in         the expiratory circuit of the ventilation circuit;     -   the brake may be an electrically operated valve;     -   the electrically operated valve may be controlled electronically         on the basis of measurements supplied by the pressure sensor;     -   the brake may comprise eyes, shutters or a diaphragm;     -   the degree of opening of the eyes or of the shutters or of the         diaphragm may be controlled electronically on the basis of         measurements supplied by the pressure sensor;     -   the system allows the generation of at least two discrete         positive expiratory pressure levels;     -   the system allows the generation of positive expiratory pressure         levels from among the levels (0; 2.5; 5; 7.5 and 10 mbar).

Another subject of the invention is a regulator the second stage of which comprises a system for controlling the expiratory pressure as claimed in any one of the embodiments of the invention.

Yet another subject of the invention is a rebreather, the rebreather comprising a system for controlling the expiratory pressure as claimed in any one of the embodiments of the invention.

The invention also relates to a self-contained underwater breathing apparatus comprising a system for controlling the expiratory pressure of a diver as claimed in any one of the embodiments of the invention.

Further features, details and advantages of the invention will become apparent from reading the description given with reference to the attached figures provided by way of example and which respectively depict:

FIG. 1: an illustration, viewed from above, of the implementation of a system for controlling expiration on a regulator according to one embodiment of the invention;

FIG. 2: an illustration in section of the implementation of a system for controlling expiration on a regulator according to one embodiment of the invention;

FIG. 3: an illustration of the implementation of a system for controlling expiration on a rebreather according to one embodiment of the invention.

As is generally accepted, diving equipment may comprise all or part of a diving hardware assembly including an isothermal suit, a mask, fins, weights, a buoyancy compensator and at least one diving cylinder containing a mixture of breathing gas, such as nitrox, heliair, hydrox, trimix, heliox and hydreliox. Usually, the gas mixture is compressed air. The diving equipment within the meaning of the invention comprises a regulator or a rebreather allowing the diver to breathe through a mouthpiece.

A regulator is a piece of open-circuit diving equipment allowing a diver to breathe the gas contained in his diving cylinder at the pressure at which he is moving around.

A rebreather is an item of closed-circuit diving equipment allowing the gas exhaled by a diver to be recirculated in order to lengthen the dive time and reduce the weight of the diving cylinders.

A self-contained underwater breathing apparatus is generally defined as being an individual device that allows its user to breathe and move around freely underwater with a reserve of compressed breathing gas.

FIG. 1 shows a view from above of the second stage of a regulator according to one embodiment of the invention. A medium-pressure gas arrives from the first stage of the regulator to the second stage via a hose 100. A knob 101 allows the flow of gas arriving in the second stage via the hose 100 to be regulated. This medium-pressure gas enters the dry chamber 102 of the second stage of the regulator and is then expanded on reaching the mouthpiece 104. It is the diver inhaling in the mouthpiece 104 that triggers the passage of the gas from the dry chamber 102 to the mouthpiece 104. The inhalation or exhalation of the diver controls, for example, the opening of a valve that allows the gas to pass from the dry chamber 102 to the mouthpiece 104 during inhalation or the gas to be blocked in the dry chamber 102 during exhalation. The pressure of the exhaled gas can be adjusted using a brake 105 and the exhaled gas is discharged from the second stage of the regulator via the twin exhalent tubes 106.

FIG. 2 shows a cross section of the second stage 20 of a regulator according to one embodiment of the invention. The arrows indicate the movement of the gas in the second stage of the regulator. In this implementation, the brake 105 comprises a calibration screw 200 and a loading spring 201. The brake 105 acts on washers 202 which act on membranes 203. The membranes 203 and the washers 202 thus form a one-way valve 204. The diver is able to act upon the calibration screw 200 to adjust the resistance of the loading spring 201. During the inhalation phase, the gas present in the dry chamber 102 enters the mouthpiece via the opening of the membranes 203. During the exhalation phase, the membranes 203 close again, completely or in part according to the resistance of the loading spring 201, and the exhaled gas is removed via the twin exhalent tubes 106. By controlling the degree of closure of the membranes, by adjusting the resistance of the loading spring 201, in order to have full or partial closure, the diver is able to alter the pressure of the exhaled gas.

The clinical manifestations of immersion pulmonary edema often occur during the reascent phase or when the diving session is extended. They do not therefore always occur at the same moment or with the same intensity in all divers. It is therefore important to be able to regulate the positive expiratory pressure as soon as symptoms start to appear, or even to anticipate the onset of edema through preventative triggering as soon as the environmental conditions become restrictive. In the embodiment described, the diver acts directly on the calibration screw 200 according to how he feels.

Furthermore, during reascent, the act of the diver adopting a more vertical attitude leads to a large difference in pressure between the regulator which is in the diver's mouth and his lungs. It is therefore necessary to generate a greater positive expiratory pressure than during descent in order to prevent immersion pulmonary edema or treat the symptoms thereof.

The second stage of the regulator may also comprise a release rod 205 which allows the brake to be deactivated, namely allows the resistance of the loading spring 201 to be canceled. This release rod 205 constitutes a safety feature regarding the solid obstruction level of the system or emergency reascent requiring the absence of any impediment to exhalation. The release rod 205 is central and coaxial with the calibration screw 200. The valve 204, the brake 105 and the release rod 205 are held in place by a fixed housing 206. This fixed housing 206 also comprises a safety release duct 207.

In a variant embodiment of the invention, a pressure sensor is positioned in the expiratory circuit to measure the pressure of the gas exhaled by the diver. According to one embodiment, the sensor may be positioned at the mouthpiece 104.

Advantageously, measurements can be collected for electronically controlling the brake 105. Electronic control of the brake allows more effective detection of any symptom associated with the onset of pulmonary edema and allows any expiratory-pressure control action to be generated more rapidly. In an embodiment involving an inbuilt sensor, the brake 105 is an electrically operated valve or solenoid valve. The brake may also be made up of eyes, of shutters or may be a diaphragm, the eyes, the shutters and the diaphragm being outlet orifices having a variable degree of opening. More generally, the brake may adopt any form that allows the degree of closing-off of the outlet area to be varied.

Thus, the system comprises two modes of operation: one referred to as passive and the second referred to as active. The passive mode is characterized by the absence of positive expiratory pressure and is the mode favored for the descent of the diver or may be the mode imposed in the event of an emergency reascent in which exhalation needs to be facilitated. The other mode of operation, referred to as active mode, is characterized by the generation of a positive expiratory pressure through the implementation of the system of the invention. The active mode is used during the diver reascent phase or when the diving session is extended. The active mode can be brought into action semi-autonomously by the diver who can regulate the level of the positive expiratory pressure by activating the calibration screw, or can be brought about automatically by being for example automatically controlled by a dive computer worn by the diver. The dive computer records the diver's diving parameters and is thus able to supply data regarding the symptoms experienced by the diver so as to activate the system for controlling the expiratory pressure. In an embodiment variant, the diving equipment may comprise a plurality of sensors allowing the supply of data which may enrich the detection of symptoms indicative of immersion pulmonary edema.

According to another embodiment of the invention, the brake 105 allows the generation of at least two discrete positive expiratory pressure levels. The 0 mbar discrete level forms one of the possible levels for the positive expiratory pressure. In order to conform to the known standards, in one embodiment, the brake allows the generation of positive expiratory pressure levels from among the following levels:

-   -   0 mbar;     -   2.5 mbar;     -   5 mbar;     -   7.5 mbar; and     -   10 mbar.

Advantageously, the positive expiratory pressure levels are chosen from among the following levels: 2.5 mbar; 5 mbar; 7.5 mbar and 10 mbar.

These positive expiratory pressure values, given by way of nonlimiting example, correspond to the levels capable of preventing the onset of pulmonary edema in emergency medicine while at the same time not achieving levels liable to create pulmonary overpressure and conforming to pressure regime limits for regulators (see standard NF EN 250, June 2014). FIG. 3 shows the implementation of one of the embodiments of the invention on a diving rebreather. The arrows indicate the movement of the gas through the rebreather. When the diver inhales, the rebreather supplies the diver with gas from the inhalation breathing sack 300. This gas reaches the mouthpiece 301 via a hose 302. In the mouthpiece 301, the inhaled gas passes through an inhalation non-return valve 303 before reaching the diver's mouth. When the diver exhales, the exhaled gas enters the mouthpiece 301 and passes through the exhalation non-return valve 304. A brake 305 that can be adjusted by the diver allows him to influence the opening of this valve 304. By limiting its opening, the brake 305 can generate a positive expiratory pressure in the mouthpiece 301, allowing immersion pulmonary edema to be prevented or treated.

Having passed through the exhalation non-return valve 304, the exhaled gas arrives at the exhalation breathing sack 306 via a hose 302. One or more breathing gas cylinders 307 supply the exhalation breathing sack 306 with breathing gas (this supply is indicated by the reference 308 in FIG. 3). The gases then present in the exhalation breathing sack 306 pass through a filter 309. This filter 309 filters out the carbon dioxide so that the gases that then enter the inhalation breathing sack 300 no longer contain carbon dioxide.

The invention has been described for a number of embodiments in order to illustrate the general principle thereof. However, those skilled in the art will be able to adapt the invention to other embodiments without diverging from the essential features described here. More generally, the invention can be used on any type of open or closed diving circuit. The embodiments described need to be considered in all respects to be purely illustrative and nonlimiting. 

1. A system for controlling the expiratory pressure of a diver for diving equipment having a ventilation circuit, comprising: a one-way valve acting on an expiratory outlet of the ventilation circuit; and a brake configured to apply an adjustable constraint to the one-way valve so as to control the pressure of the gas coming from the expiratory outlet so as to generate a positive expiratory pressure in said breathing circuit.
 2. The system for controlling the expiratory pressure of a diver as claimed in claim 1, wherein said brake is an adjustable discharge valve comprising a loading spring and a calibration screw allowing the resistance of said spring to be adjusted.
 3. The system for controlling the expiratory pressure of a diver as claimed in claim 1, additionally comprising a release system allowing said brake to be deactivated.
 4. The system for controlling the expiratory pressure of a diver as claimed in claim 3, wherein the release system comprises a central tubular rod coaxial with said calibration screw.
 5. The system for controlling the expiratory pressure of a diver as claimed in claim 1, additionally comprising a pressure sensor sensing pressure in the expiratory circuit of said ventilation circuit.
 6. The system for controlling the expiratory pressure of a diver as claimed in claim 5, wherein the brake is an electrically operated valve, the electrically operated valve being controlled electronically on the basis of measurements supplied by the pressure sensor. (Original) The system for controlling the expiratory pressure of a diver as claimed in claim 6, wherein the brake comprises eyes or shutters or a diaphragm.
 8. The system for controlling the expiratory pressure of a diver as claimed in claim 7, wherein the degree of opening of the eyes or of the shutters or of the diaphragm is controlled electronically on the basis of measurements supplied by the pressure sensor.
 9. The system for controlling the expiratory pressure of a diver as claimed in claim 1, wherein the brake allows the generation of at least two discrete positive expiratory pressure levels.
 10. The system for controlling the expiratory pressure of a diver as claimed in claim 1, wherein the brake allows the generation of positive expiratory pressure levels from among the levels (0 mbar; 2.5 mbar; 5 mbar; 7.5 mbar and 10 mbar).
 11. A regulator for diving, comprising at least: a first stage for expanding a high-pressure gas in order to obtain a medium-pressure gas, and a second stage able to receive said medium-pressure gas and drop the pressure of said medium-pressure gas in order to supply low-pressure gas to a diver who can be ventilated, wherein the second stage of the regulator comprises a system as claimed in claim 1 for controlling the expiratory pressure of the diver.
 12. A rebreather for diving comprising a system for controlling the expiratory pressure of a diver as claimed in claim
 1. 13. A self-contained underwater breathing apparatus comprising a system for controlling the expiratory pressure of a diver as claimed in claim
 1. 